When += (and similar operations) are converted to = + ,

frog/gen.dart

Index: frog/gen.dart
===================================================================
--- frog/gen.dart	(revision 2468)
+++ frog/gen.dart	(working copy)
@@ -1870,7 +1870,10 @@
         return;
       }
       return x.invoke(this, name, node, new Arguments(null, [y]));
-    } else {
+    } else if ((assignKind != 0) && (node.y is BinaryExpression)){

[jimhug, 2011/12/15 17:58:10]

Final comment: Please add a TODO or unify with parenthesis adding code in
visitLiteralExpression.  I think that some of those MAY be relevant here as well
- but more significantly, this is hard enough that we should be only doing it in
one place.

[dgrove, 2011/12/15 20:55:51]

Done.

+      return _visitAssign(assignKind, node.x,
+          new ParenExpression(node.y, node.y.span), node, null, isVoid);
+    } else {  
       return _visitAssign(assignKind, node.x, node.y, node, null, isVoid);
     }
   }